Wireless digital networks, such as networks operating under the current Electrical and Electronics Engineers (IEEE) 802.11 standards, are spreading in their popularity and availability. Currently, in a wireless local area network (WLAN), specialized hardware sensory devices are deployed at different physical locations for various purposes, for example, power optimization, security surveillance, emergency service, etc. These sensory devices usually are battery-powered or have their own power supply cables rather than Power over Ethernet (PoE) ports for receiving power.
Conventionally, detecting physical activity in an environment for security surveillance is achieved by detecting a Doppler shift in the carrier frequency by specialized hardware devices. A Doppler shift generally refers to a change in the carrier frequency because one or more objects have moved in the environment. Adding functionality of detecting Doppler shifts to access points would require adding specialized hardware components to a WLAN chipset, which would incur an additional cost. Moreover, additional hardware component on the WLAN chipset would also result in more power consumptions. With PoE enabled, it is important for an access point to conserve power consumptions. Thus, given the cost and power limits mentioned above, a typical WLAN chipset has no functionality of detecting Doppler shifts to avoid sacrificing basic functionalities.